1. The Field of the Invention
The present invention relates generally to multichip semiconductor packages and particularly relates to an improved semiconductor package having a plurality of semiconductor chips fabricated as a singular coextensive substrate and to its method of making.
2. The Relevant Technology
Multichip packaging is one of the fastest growing disciplines in the chip packaging industry. Initially, the multichip package came into existence for applications requiring numerous and varied circuits configured into a least amount of space, such as with mainframes and supercomputers. Since then, multichip packages have transcended traditional boundaries and moved into conventional single-chip applications because they characteristically possess reduced weight and size per each circuit, increased reliability and increased electrical performance. As such, multichip packages are now regularly employed in consumer electronics, medical and avionic devices, and in the automotive and aerospace industries. Multichip packages also find particular usefulness in telecommunication applications because of their high bandwidth performance.
In general, conventional multichip packages are available in one of two varieties. One has two or more bare chips bonded directly to a multichip substrate and the other, the most commercially predominant package, having two or more pre-packaged single-chips, in their respective single-chip carriers and bonded to a multichip substrate. Although the former variety enjoys advantages over the latter, both varieties remain bound by single-chip constraints because of their dependence upon either a bare, or packaged, single-chip. As such, both varieties frequently share common problems with their single-chip counterparts.
For example, in response to an industry-wide demand for high lead counts and small "footprints," i.e., the arrangement of electrical contacts on the printed circuit board to which the chip package is ultimately connected, single-chip packages became available in Ball Grid Array (BGA), "flip-chip" and "chip-scale" packages. The problem, however, is that these singular-chip packages have external electrodes, which can be solder balls, that are directly attached to contacts on the surface of the semiconductor chip. As semiconductor chips are continually reduced in size, the arrangement of the external electrodes must also be continually reconfigured into a correspondingly smaller size. In turn, the footprint on the printed circuit board must also be continually reconfigured. This problem is even further amplified with multichip packages because footprint reconfiguration also needs to occur on the multichip substrate itself to which the single-chip packages are attached. It is, therefore, desirous to eliminate the continual reconfiguring of the footprint of the multichip package and the rearrangement of the multichip substrate.
In a separate and distinct discipline, Wafer Scale Integration (WSI) techniques have been used to fabricate various other multichip arrangements. Yet WSI often utilizes 800, or more, semiconductor chips as a single multichip which, in effect, is too cumbersome, if not prohibitive, to encapsulate into a package format. The large size is also inefficient for applications requiring relatively few semiconductor chips, around 64 or less, because of the high wiring density used in WSI wirebonding operations and the surplus unneeded chips. Effective testing of each individual chip with WSI is also problematic because of the large number of chips. Additionally, WSI techniques frequently require expensive photolithography equipment, not typically utilized with single-chip packages, to transfer a circuit image onto a multichip substrate.
A need exists for a multichip package that overcomes the foregoing problems.